A CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) scheme has been adopted as an access control scheme of a radio communication system.
In the radio communication system adopting the CSMA/CA scheme, however, when a plurality of radio terminal devices are about to simultaneously transmit radio frames to an identical access point under an environment in which the radio terminal devices cannot recognize each other, a collision of the radio frames from the individual radio terminal devices may take place. This problem is called the “hidden terminal problem”.
The communication throughputs of the individual radio terminal devices in the radio communication system lower due to the collision of the radio frames.
In order to solve this problem, there has been used a technique wherein the communications between the radio terminal devices and the access point are appointed beforehand by utilizing RTS (Request To Send)/CTS (Clear To Send) functions.
In case of applying the RTS/CTS functions, each radio terminal device transmits an RTS packet that contains a scheduled appointment period to the access point before the radio terminal device transmits data to the access point. Upon receiving the RTS packet, the access point transmits CTS packets to the individual radio terminal devices. The radio terminal device having transmitted the RTS packet starts the data transmission by receiving the CTS packet from the access point. On the other hand, any other radio terminal device not having transmitted the RTS packet becomes incapable of transmitting data during the scheduled appointment period designated by the received CTS packet, when the other radio terminal device has received the CTS packet.
Owing to the utilization of the RTS/CTS functions, the collision of the radio frames is avoided, and hence, the “hidden terminal problem” is eliminated. On the other hand, however, the lowering of the communication throughputs poses a problem.
In this regard, there has been adopted a scheme that asserts the RTS/CTS functions in a case where the packet to be transmitted is equal to or larger than a predetermined size, and which negates the RTS/CTS functions in a case where the packet to be transmitted is smaller than the predetermined size. A value that determines the assertion/negation of the RTS/CTS functions, shall be called the “RTS/CTS threshold value” below.
Regarding the above technique, it has been known to properly use a multiple access scheme of collision channel and a multiple access scheme of non-collision channel in accordance with a communication traffic.
Also, a radio packet communication system including radio terminal devices each of which transmits an appointment signal in accordance with a transmission data quantity, and an access point that switches a contention mode and a polling mode on the basis of information obtained by totaling and averaging appointment quantities from the radio terminal devices has been known.
The following documents are documents which disclose techniques concerning communication systems:    Patent Document 1: JP-A-08-274788    Patent Document 2: JP-A-09-135248
However, there is no definite setting criteria for the RTS/CTS threshold value. Therefore, it has been difficult to determine the RTS/CTS threshold value suitable for the radio communication system.
Thus, various embodiments described herein determine the optimum RTS/CTS threshold value in accordance with a radio communication system.